The invention relates to a method for recovering heat dissipated by an internal combustion engine, in which a working medium is first compressed in a compressor, subsequently evaporated in a heat exchanger by heat transfer from a heat medium containing heat dissipated by the internal combustion engine. Then the vapors are expanded in an expansion device, while mechanical power is recuperated in the expansion device, and subsequently the expanded vapor is condensed in a condenser. The invention further relates to a device for carrying out the method.
Present-day internal combustion engines have a degree of efficiency of up to 40 percent. The losses are thereby mainly passed on to a coolant and to the exhaust gas of the internal combustion engine as waste heat.
In the state of the art different methods and devices exist, by means of which mechanical and/or electrical energy can be obtained from an exhaust gas heat and/or a coolant heat of an internal combustion engine.
EP 1 443 183 A1 discloses a heat recovery device based on a Clausius-Rankine cycle process, with which energy can be obtained from an exhaust gas heat of an internal combustion engine. The heat recovery device comprises a delivery unit, a heat exchanger, an expansion device and a condenser, which are interconnected in a circuit and in which a working medium can be circulated. Further, means are provided with which a temperature of the working medium behind the heat exchanger can be adjusted in dependence on, a temperature of the working medium in front of the heat exchanger and on a mass flow of the working medium. The device further comprises means for adjusting a pressure of the working medium prior to the entry into the expansion device in dependence on the temperature of the working medium behind the heat exchanger.
T. Endo, S. Kawajiri, Y. Kojima, u. a. (Honda R&D Co., Ltd.): Study on Maximizing Exergy in Automotive Engines; in SAE TECHNICAL PAPER SERIES 2007-01-0257; 2007 World Congress, Detroit Mich., Apr. 16-19, 2007 discloses a heat recovery device, which can also be operated according to the Clausius-Rankine principle. The device comprises a delivery unit, a heat exchanger, an expansion device and a condenser, which are interconnected in a cycle and are flown through by a working medium. The device further contains a regulation unit, with the help of which a temperature of the working medium behind the heat exchanger can be regulated to a fixed target value. A speed of the delivery unit or a mass flow of the working medium through the heat exchanger thereby serves as a variable. Furthermore, a pressure of the working medium in front of the expansion device can be regulated to a fixed target value by means of a further regulation unit, wherein a speed of the expansion device is provided as variable.
It is the object of the present invention to provide a method for recovering heat dissipated by an internal combustion engine, with an optimum degree of efficiency during various operating conditions of the internal combustion engine. It is also an object of the present invention to provide an internal combustion engine with a heat recovery device for carrying out the method.